This application is entitled to the benefit of, and incorporates by reference, essential subject matter disclosed in German Patent Application No. 101 06 234.6 filed on Feb. 10, 2001.
The invention concerns a piston compressor, particularly a hermetically enclosed piston compressor, with a housing, in which a motor is arranged, the motor having a crankshaft with a vertically standing crank pin that has in its upper front side an opening, which is connected with an oil supply arrangement.
A compressor of this kind is known from DE-OS 22 32 430. Here, the crankshaft has an axial through-bore, whose lower end opens into a hollow cone, which is immersed in an oil sump. At the upper end, the through-bore is connected with an inclined bore, which ends at the front side of the crank pin. On a rotation of the crankshaft, lubricating oil is discharged from the oil sump by means of centrifugal force and supplied to the front side of the crank pin. The crank pin is surrounded by a bushing, in which an oil reservoir can build up. On rotation of the crankshaft, the oil available in the oil reservoir moves on the inside of the housing by means of centrifugal force, where it can release heat to the environment, when flowing back to the oil sump by way of gravity. In a predetermined circumferential section, the bushing has an axial extension, which is directed so that the oil cannot immediately be spun onto the cylinder block. Thus, this extension causes the centrifuged oil to be transported past the cylinder head before reaching the inner wall of the housing.
U.S. Pat. No. 4,569,639 A shows another refrigerant compressor with an oil pipe, fixed with one end in the front side opening of the crank pin. The other end of the oil pipe can now be directed so that the oil cannot be centrifuged onto the top wall of the housing, but only onto the circumferential wall. Further, the oil pipe has a radial bore, which permits oil to escape in the direction of the cylinder head, in which an oil distribution arrangement is arranged, which distributes the oil over the whole cylinder head.
In both of the above-described cases, it can be observed that an unacceptable amount of oil is sucked into the suction muffler and the cylinder together with the suction gas. After compression, this oil reaches the refrigeration system, which is supplied by the piston compressor. This phenomenon is known as xe2x80x9cexternal oil circulationxe2x80x9d. However, external oil circulation has several disadvantages. First, under unfavourable circumstances, so much oil can be removed from the oil sump of the compressor that a sufficient lubrication of the moving parts in the compressor is no longer ensured. Second, the refrigeration performance of the complete refrigeration system is deteriorated, as the oil reduces the heat transfer coefficients in the heat exchangers. This applies for both the evaporator and the condenser. The free flow cross section for the refrigerant in the capillary tubes of the system can be reduced, which could, in the extreme case, cause a complete choking of the thin tubes.
Thus, the invention is based on the task of reducing the external oil circulation.
With a piston compressor as mentioned in the introduction, this task is solved in that the opening is provided with a limiting arrangement, which limits an axially directed movement of lubricating oil from the opening in a predetermined area.
Due to the limitation of the axial movement, it is now possible to exclude certain areas of the inner wall of the housing completely from an oil supply. This is independent of the speed of the crankshaft. Thus, an area of the inner wall of the housing can intentionally be kept free of oil.
For example, it can be avoided that oil reaches the part of the housing wall situated directly over the suction fitting and drops down on the mouth of the suction fitting. If this was the case, large amounts of oil particles would be carried along by the suction flow and get into the suction muffler. Such a case is particularly problematic with compressors with so-called direct suction, whose suction fitting is connected direct with the inlet of the suction muffler by means of a flexible connection. Often, the flexible connection is realised by means of mutually displaceable telescopic pipes, in order to avoid that vibrations, which particularly occur in connection with turning on and turning off, cause line ruptures. However, the telescopic connections cannot be made completely tight.
A further complication occurs in that the pressure inside the housing is slightly higher than the suction pressure in the suction line, meaning that oil is practically sucked into the suction gas flow from the housing interior, when the oil is permitted to come close to leaky connections. When, however, it is ensured that the oil flow is kept away from such critical spots, the risk of oil reaching the refrigerant circuit is greatly reduced. By means of the specific screening of the oil, it can also be prevented that the cylinder head is sprayed with the lubricating oil. Also this serves the purpose of preventing the penetration of oil through the connections between the suction muffler and the valve plate. For tolerance and assembly reasons, the connections cannot always be made completely tight. In this connection, the opening can be made direct in the front side of the crank pin. However, it is also possible, and in many cases also preferable, that the front side is surrounded by a bushing, whose upper edge forms the opening.
Preferably, the limiting arrangement is in connection with the edge of the opening. The limiting arrangement can, for example, have an axially extending wall, which extends the edge of the opening on part of its circumference. Thus, further to the axial limitation of the centrifuged oil, also a radial limitation of the oil flow can be realised. The areas, which can be kept free of oil, can thus be chosen even more specifically.
Preferably, the limiting arrangement has a deflector element, which faces the front side. This is a relatively simple design of a limiting arrangement. The deflector element partly covers the opening in the axial direction, if required, at a distance. When the oil reaches the deflector element, it is retarded and led back to the oil reservoir, which has built up at the opening in the front side of the crank pin. Additionally, this arrangement involves the advantage that the energy is not lost, which had to be procured to transport the oil to the opening. The oil retarded by the deflector element is then supplied to another place in the housing.
Preferably, the limiting arrangement is arranged to be unrotatable in relation to a connecting rod, which cooperates with the crank pin. On the one hand, the connecting rod produces a spatial allocation between the limiting arrangement and the crank pin, to ensure that also on a rotation of the crankshaft the limiting arrangement always remains in the correct position in relation to the crank pin and the opening. On the other hand, the placing of the limiting arrangement on the connecting rod ensures that during a rotation of the crankshaft a predetermined angle area is always prevented from delivering oil. In a manner of speaking, this angle area is the shadow area, which the limiting arrangement creates on one rotation. Adjacent areas will receive less oil during a rotation of the crank pin. However, they are still supplied with oil.
Preferably, the extension of the deflector element in parallel to the front side corresponds to a circle sector. The extension can also be denoted as a projection perpendicular to the front side or as a cross-section in parallel to the front side. The side of the extension, facing the front side, can be convex, one-side or multi-side inclined or plane. The sector ensures a complete covering of the predetermined area, also at relatively high speeds of the crankshaft. Of course, also other embodiments are possible, for example a circle section or an annulus. However, it must be ensured that also with maximum speed of the crankshaft no oil is transported past the deflector element and into the predetermined area, which are to be excluded from an oil supply.
Preferably, the limiting arrangement is made as a put-on part, which is fitted on the connecting rod. This embodiment involves advantages with regard to costs and assembly, as basically, the limiting arrangement does not have to be fitted until the crankshaft, the connecting rod, the piston and the cylinder block have been assembled.
Preferably, the put-on part is in the form of a cylindrical bushing, which is fitted on a connecting rod eye that surrounds the crank pin. Such a part is easily manufactured, for example from metal. Preferably, however, a temperature, oil and refrigerant resistant plastic is used, if required in a reinforced form. Then, the put-on part can be made by means of injection moulding.
Preferably, the put-on part forms a snap connection together with the connecting rod eye. This simplifies the mounting, and ensures a reliable retaining of the put-on part in the desired position.
It is also advantageous, when the limiting arrangement is oil permeable in an area, which is directed towards the connecting rod. In spite of the screening, it is desirable and advantageous to lubricate and cool the reverse of the piston, the bolt bearing between the connecting rod and the piston bolt as well as the rear end of the cylinder wall surface by means of an oil jet. This improves the lubricating and wear conditions and causes an improved sealing of the compression chamber. Accordingly, a smaller amount of refrigerant penetrates through the gap between the piston and the cylinder during the compression process, which means that the efficiency of the compressor is improved. In fact, it is sufficient that in this spot the limiting arrangement has a hole or another opening, through which the oil jet can pass. A side effect of this hole is that the limiting arrangement, particularly when being in the shape of a put-on part, is easier to widen in the radial direction by this hole, so that it can more easily be fitted on to the connecting rod eye.
Preferably, the crank pin is surrounded by a rotatable bushing, which projects axially over the crank pin and forms a vessel, the bushing being unrotatably connected with the connecting rod eye and having an auxiliary opening, which is directed towards the connecting rod. Now, the oil jet cannot only be realised in that the oil runs over the edge of the opening and then passes through the limiting arrangement, but also more specifically in that the bushing has the auxiliary opening, the limiting arrangement not being permitted to form any objection for the oil jet in the area of the auxiliary opening.
Preferably, the auxiliary opening is in the shape of a slot. Then, on the one hand, it can be made large enough to let sufficient oil pass. On the other hand, the spatial extension of the oil jet will be limited, so that it can be directed relatively accurately to the spots to be lubricated.